Genetic Mapping Reveals a Major QTL Associated with Tolerance to the Aphid, Uroleucon Compositae (theobald) in Safflower (carthamus Tinctorius)

Host plant resistance is an effective means of managing aphid pests in safflower but its genetic basis is not known. In this study, F-1 and F-6-recombinant inbred lines (RILs) produced from the CO-1 x EC-523368-2 cross were phenotyped for tolerance to the aphid, Uroleucon compositae based on days-to-wilt (DW) after infestation. The F-1 plants showed the dominance effect and RILs exhibited quantitative variation. The RIL population was genotyped with 242 simple sequence repeat (SSR) markers, which included a set of 150 new SSRs designed through next-generation sequencing and bioinformatics approaches. Two quantitative trait loci (QTLs), QUc-Ct3.1 and QUc-Ct5.1, putatively associated with DW after aphid infestation were detected. QUc-Ct3.1 was a major QTL located on linkage group (LG) 3 with the closest marker SafM-290 (LOD = 18.3), which explained 31.5% of the phenotypic variation. QUc-Ct5.1 was a minor QTL located on LG-5 with the closest marker CtDES-237 (LOD = 7.0), which explained 9.1% of the phenotypic variation. This is the first report and a significant lead towards discovering genes for tolerance to aphids in safflower.